35) 1 Gases are separated from liquid air by fractional distillation. The boiling points of four gases are shown.
Which gas is both monatomic and a liquid at -200 °C?
gas
boiling
point/°C
A
argon
-186
B
helium
-269
с
neon
-246
D
nitrogen
-196

1. 1 mole of anything contains 6.022x10^23 pieces  

d  

2. a  

3. c, number  

5. 1.24x10^24atoms / 6.022x10^23atoms/mole = 2moles h2 atoms  

6. fe2br3 mass = 2moles x mass fe + 3 moles x mass br  

molar mass = grams / number of moles = g/mole  

to find moles = g / molar mass  

to find mass = g = molar mass / moles